A compression connector typically includes a hollow tubular section which is deformed with a special tool. The tool compresses the outer periphery of an electrical connector onto a stranded electrical conductor.
Typically, in transmission lines, stranded electrical conductors are utilized. Stranded electrical conductors have a steel core overlaid by one or more layers of conductive aluminum stranding. These cables have multiple layers of individual strands. The individual strands are laid in an opposite direction to an adjacent underlying layer, making each layer distinctive from its adjacent layer by its direction.
The advent of increasing power demands results in electrical connectors being operated at much higher current levels. Consequently, higher current levels result in much higher temperatures. The increased load on the electrical grid amplifies the current density and thermal stress of the entire system. Therefore, compression connectors, are weak links in the system, and are failing at an increasing rate.
The majority of failures occur in aluminum compression connectors and conductors. The reasons for these failures are two-fold. First, the vast majority of new connectors and conductors being installed are aluminum. Second, high integrity aluminum connections are difficult to achieve due to oxidation. Aluminum oxide is a highly effective electrical insulator, and is detrimental to the integrity of a compression connector on an aluminum conductor.
Aluminum has a very high chemical affinity with oxygen, causing aluminum oxide to form easily. By simply exposing aluminum to air, a very thin oxide film will form on the aluminum surface. As a result, oxide layers forming on both the cable and connector are a reason for concern. Conductivity of the electrical interface between the connector and the conductor is severely reduced when oxides are present.
The surfaces of the conductor stranding are continuously exposed to oxygen. Consequently, an oxide coating forms on the conductor stranding and must be penetrated during the installation process to form an electrical connection. Compression connectors only make contact with the outermost periphery of the conductor stranding and cannot physically access the inner layers. Thus, penetrating the oxide coating on the inner layers improves the integrity of the connectors.
Presently, the most effective method of cleaning the conductor is to unlay the strands of the outer layers. The inner layers are exposed and are cleaned by vigorous brushing. Consequently, the formation of tenacious, highly resistive aluminum oxide is reduced.
The problem with this cleaning method is that it is highly time consuming and very difficult to accomplish in the field. The process of unlaying the stranding of the conductor a sufficient distance from the end to allow cleaning of individual stranding is laborious and tedious. While this method is possible in a typical laboratory condition, where the conductor may remain supported and still, the method is often unsuccessful in the field. Performing the cleaning steps successfully on an aerial platform, such as a bucket truck, is highly improbable due to difficultly to dealing in handling the individual conductive strands. The strands must be held in a suitable manner to brush them with sufficient force to effectively remove the oxide layer. Therefore, this method typically is not done in the field.
In addition, difficulties arise when the strands are re-layered into their original position. Compression connectors are designed with minimal space to receive the design standard of the outer diameter of the conductor. Consequently, if the strands are not re-layered to provide the original diameter of the conductor as manufactured, the conductor cannot be inserted into the compression connector designed therefore.
Additionally, the above method does not solve the problem of the rapid formation of oxides. After the stranding is brushed and a large portion of the old oxide coating removed, new oxides form immediately on the clean surfaces exposed to oxygen. The newly formed oxides formed on the surface of the aluminum strands prevent the passage of current between the innermost strands of the conductor through each successive layer and the compression connector.
Another prior art cleaning method requires the use of an abrasive material such as a sand paper. The sand paper is wrapped about the periphery of each individual strand for abrading the oxide layer. However, the abrasive material will also wipe away the oil coating of the inhibitor designed to provide the oxygen barrier needed to prevent the re-growth of the oxide layer which the cleaner is attempting to remove.
Lastly, abrasive inhibitors are also used to enhance the electrical performance of connectors. During the compression process, a gritted inhibitor is forced hydraulically through interstitial spaces between the strands. The inhibitor abrades the oxide layer as it progresses. However, this method works well only on the outer layer. Rarely, does any significant amount of the gritted inhibitor find its way to the inner layer interstices. Thus, the current being carried by the inner layers of the conductor meets a high resistance interface. As a result, the outer layers have higher current densities and increase the temperature of the conductor, particularly at the connector interface.
While the aforementioned methods help to some degree, nonetheless a continuing recurrence of connector failures in electrical grid infrastructures necessitate improvements to enhance the integrity and longevity of the electrical connectors of the infrastructure.
Thus, a continuing need exists to provide improved compression connectors.